Mechanistic Study of Ethanol Decomposition on Co3O4(111) and Pd/Co3O4(111) Model Catalysts

In many advanced catalytic materials, different functionalities are coupled through spillover of active species across heterogeneous interfaces. In the present work, we consider the coupling of a C & horbar;C bond cleavage functionality of palladium with the self-cleaning functionality of reducible Co3O4. On the model catalyst Pd/Co3O4(111)/Ir(100), we probed the interplay of the two functionalities for the selective decomposition of ethanol. In a systematic study, we compared the decomposition mechanisms of ethanol on Co3O4(111)/Ir(100) and Pd/Co3O4(111)/Ir(100) model catalysts using a variety of analytical techniques including synchrotron radiation photoelectron spectroscopy (SRPES), resonant photoemission spectroscopy (RPES), temperature programmed desorption (TPD), and near ambient pressure X-ray photoelectron spectroscopy (NAP-XPS). We found that ethanol decomposes via an ethoxy intermediate yielding acetaldehyde on Co3O4(111)/Ir(100). Remarkably, the spillover of ethanol/ethoxy species on Pd/Co3O4(111)/Ir(100) results in the selective formation of methane, hydrogen, and CO. Additionally, we observed CO2 resulting from the oxidative removal of carbonaceous deposits on Pd nanoparticles via spillover of active oxygen species released by Co3O4(111)/Ir(100) at higher temperatures. The onset of product formation and the product spectrum on both Co3O4(111)/Ir(100) and Pd/Co3O4(111)/Ir(100) depend strongly on the oxidation state of Co3O4. Complete removal of lattice oxygen from Co3O4(111) results in the deposition of large amounts of carbon.